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Friday, December 31, 2010

Secret Lives of Baby American Beavers Filmed - BBC - Earth News

Using discreet video cameras, scientists have been able to study the long-term natural behaviour of beavers "at home" in their lodges.

The tiny, waterproof cameras, inserted into beaver dens, show that beavers lead very different private lives when at home than when outside.

At home, the animals are surprisingly co-operative and scientists have even recorded baby beavers growing up.

Kits exhibited multiple sleep wake cycles lasting only a few hours, much like a human infant waking up every few hours during the night - Professor Cy Mott

"Much of what we know about beavers and their use of dens is limited to questions like 'what times of day do they go in and out of the den'", says Cy Mott, a biologist at Kentucky Wesleyan College, in Owensboro, US.

"Simply because, until recently, we haven't had the technology to follow their behavior within the den without potentially disturbing natural behaviour."

So Professor Mott and colleagues, Craig Bloomquist and Clayton Nielsen of Southern Illinois University in Carbondale, US, decided to study American beavers ( Castor canadensis ) denning on the Mississippi flood plain in south-western Illinois.

Beavers in this region declined drastically in the 19th and 20th Centuries, but have since recovered due to a ban on hunting them for their pelts.

The researchers used special "probe" cameras that do not disturb the beavers to record the animals' behavior in 23 colonies over the course of more than a year.

Beavers make sophisticated homes, either in dens burrowed into river banks, or more complex lodges.

Lodges are essentially dens built from wooden branches that are surrounded by water, the level of which beavers help maintain by also building wooden dams.

Video taken of beavers within 17 lodges and six bank dens revealed some surprising behaviours.

Living in their elaborate shelters, beavers were thought to be cut off from the outside environment.

But the video study shows that they exhibit regular patterns of behaviour, leaving to feed at roughly the same time every day, for example.

"This suggests that they may not be as cut off from the external environment as we think they are," says Professor Mott.

Male and female beavers appear to take equal responsibility for raising their babies, known as kits, perhaps because the young are so "high maintenance".

In the privacy of their own home, beavers also spend 95% of their time feeding, sleeping, and grooming.

"It supports the assumption that the relative security of the den is a place where they can exhibit behaviors that would be potentially dangerous outside of dens," says Professor Mott.

Baby Sleep

Another surprise relates to the private lives of baby beavers, and their sleeping patterns.

Baby beavers, and adults, follow a similar sleep schedule to humans, the researchers report in the journal Mammalian Biology.

Adults beavers tended to sleep at a similar time, though not all the adults fall asleep at once, perhaps to ensure the babies are looked after.

"Kits, on the other hand, exhibited multiple sleep wake cycles throughout the day and night, with each interval lasting only a few hours, much like a human infant waking up every few hours during the night," says Prof Mott.

Finally, "given that beavers are in incredibly close confines within dens, we fully expected to document aggressive behaviours," he explains.

Most social animals that live in close-knit groups tend to use aggression to establish a "pecking order" between individuals.

But "one of the most interesting things we didn't find was aggression within beaver colonies," Prof Mott told the BBC.

The researchers know of only two previous studies that attempt to explain what happens within a den, despite the fact that beavers spent considerable portions of their lives in these structures.

In one study, scientists cut away one side of a lodge to view the beavers directly via a glass panel, which likely disturbed the animals' natural behavior.

The other study consisted of a researcher "listening in" while outside the lodge, in an attempt to describe what was happening inside.

"To our knowledge, our study is the first to use long-term video data to follow behavior for months at a time, over successive years, and even during the period from birth of beaver kits until they disperse to find territories of their own," says Professor Mott.

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